The name VR6 comes from a combination of V engine (German: V-Motor), and the German word "Reihenmotor" (meaning "inline engine" or "straight engine") - and so is described as a "Vee-Inline engine" (VR-Motor). It shares a common cylinder head for the two offset banks of cylinders. It has a specific sound that is unique and different than either inline or "V" engines. The engine is currently in use in a variety of VW models, one such example is the Volkswagen Passat NMS.[1]

This engine configuration was also adopted for the Horex VR6 Motorbike.

The Volkswagen VR6 was specifically designed for transverse engine installations in front-wheel drive vehicles. The narrow angle of 15° between the two 'rows' in the VR6 engine is a more compact size than a wider angle V6 design. This made it possible for Volkswagen to install six-cylinder engines in existing four-cylinder cars. The wider configuration of a wider angle V6 engine would have required an extensive redesign of the vehicles to enlarge the engine compartment. The VR6 is also able to use the firing order of a straight-six engine.

The narrow angle between cylinders allows the use of just one cylinder head - whereas wider angle Vee engines require two separate cylinder heads, one for each cylinder bank. The VR6 arrangement needs two overhead camshafts to drive all the valves, regardless of whether the engine has two valves per cylinder, or four per cylinder. This simplifies engine construction and reduces costs. In early VR6 engines with 12 valves (two per cylinder) two overhead camshafts were used. The forward camshaft (in the transversely mounted engine) has six cam lobes to control the three intake and three exhaust valves of the front cylinder bank, without using rockers. The rear camshaft is designed the same way, but controls the rear cylinder bank. The operating principle of this design is comparable to a single overhead camshaft (SOHC) design with intake and exhaust valves of one bank driven by one camshaft. The later VR6 engine designs with 24 valves (four per cylinder) had two overhead camshafts as well, however with a slight change of operation principle: In the 24 valve engine all intake valves are operated by the front camshaft (with the aid of rockers), while all the exhaust valves are operated by the rear camshaft (again with rockers). This operating principle is more akin to a double overhead camshaft (DOHC) design, with one camshaft for intake valves, and one for exhaust valves.

There are several different variants of the VR6 engine. The original VR6 engine displaced 2.8 litres and featured a 12 valve design (two valves per cylinder). These engines produced a DIN-rated power output of 128 kW (174 PS; 172 bhp), and 240 N·m (177 lbf·ft) of torque.

Volkswagen Group identifies the original VR6 by the chassis "AAA" engine ID code. It operates on the four-stroke cycle, and has an engine displacement of 2.8 litres. The 2.8 VR6 cylinder bore diameter is 81.0 millimetres (3.19 in), and the pistonstroke is 90.0 millimetres (3.54 in), although some European engines had a displacement of 2.9 litres (this variant identified by the "ABV" engine ID code). The 2.9 VR6 cylinder bore diameter is 82.0 millimetres (3.23 in), and the pistonstroke is 90.0 millimetres (3.54 in). The "Vee" angle is 15°, and the compression ratio (CR) is 10:1.[2]

Schematic diagram showing the differences in port lengths between a V6 and VR6 using 12-valves

Schematic diagram showing the differences in port lengths between a V6 and VR6 using 24-valves

Because of the cylinder arrangement in the VR6 - with two rows of combustion chambers within the same cylinder head, the intake and exhaust ports between the two rows of cylinders are of varying lengths. Without compensation, these varying port lengths would result in the two rows of cylinders producing different amounts of power at a particular engine RPM. Depending on the specific generation of VR6, the difference in port lengths are compensated for by specific tuning of the intake manifold, the camshaft overlap and lift profile, or a combination thereof.[5]

The fuel injectors, operated by the BoschMotronicengine control unit (ECU) system, are mounted behind the bend of the intake manifolds. VR6 engines also use an auxiliary electric pump to circulate the engine coolant whilst the engine is running, and also during the cooling fan 'after-run' cycle, in addition to the belt-driven main water pump.

The centerline of the cylinders are also offset from the centerline of the crankshaft by 12.5 millimetres (0.49 in). To accommodate the offset cylinder placement and narrow "Vee" design, the connecting rod bearing journals are offset 22° to each other. This also allows the use of a 120° firing interval between cylinders.[6] The firing order is: 1, 5, 3, 6, 2, 4.[7]

The Volkswagen Group VR6 engine was introduced in Europe by Volkswagen in 1991, in the Passat and Corrado; and in North America the following year. The Passat, Passat Variant (estate/wagon), and U.S.-specification Corrado used the original 2.8 litre design; the European-specification Corrado and the 4WD Passat Syncro received a 2.9-litre version with 140 kilowatts (190 PS; 188 bhp). This version also had a free flowing 6 centimetres (2.4 in) (2.5 in) catalytic converter, sharper camshafts, 4-bar (58 psi) fuel pressure regulator, enlarged inlet manifold, and larger throttle body. It was also sold to Mercedes Benz for use in their vans, and designated as M104.900.

The 2.9-litre engine, as destined for the Corrado, was originally designed to benefit from a dual-tract variable-length inlet manifold - called the VSR (German: "Variables SaugRohr"), and made by Pierburg for Volkswagen Motorsport. This gave extra low-down torque, but was deleted before production on cost grounds, and was instead offered as an aftermarket option. This design was later sold to Schrick, who redesigned it and offered it as the Schrick VGI ("Variable Geometry Intake").

In 1992, with the introduction of the Volkswagen Golf Mk3, a six-cylinder engine was available for the first time in a lower-midsize segment hatchback in Europe. North America waited until 1994 to receive this engine; at the same time, the European model started to use the 2.9-litre in the VR6 Syncro model. The corresponding Vento/Jetta VR6 versions appeared in the same years.

Volkswagen Group removed a cylinder from the VR6 in 1997 to create the VR5 (aka 'V5'), the second block to use an uneven number of cylinders in a Vee design after the Honda V3 triples of MotoGP fame. This version, which had a 2.3-litre capacity, was capable of 110 kilowatts (150 PS; 148 bhp), and had a maximum torque of 210 newton metres (155 lbf·ft). It was introduced in the Passat in 1997, and the Golf and Bora in 1999.

Further modifications were added to the design in 1999, with the introduction of the 24-valve 2.8-litre VR6. This engine produced 150 kilowatts (204 PS; 201 bhp), and 265 newton metres (195 lbf·ft) of torque. The new version was not available in the Passat (as it was incompatible with the then-current generation's longitudinal engine layout), but was introduced as the range-topper in the Golf and Bora for European markets under engine codes AQP and AUE from 1999. The VR6 name was dropped as a commercial designation,[citation needed] and the 4WD system (now renamed 4motion) became standard on the V6 (VR6) in Europe. The corresponding multi-valve V5 was only released in 2001, with a 20 PS power increase, to 125 kilowatts (170 PS; 168 bhp). The multi-valve V6 (VR6) was introduced in North America in 2001 aboard the T4 Eurovan, producing 150 kilowatts (204 PS; 201 bhp), and in the GTI in 2002 (where it retained the VR6 name).

In 1999, an updated 12-valve VR6 model was released for the North American market A4-platformGolf Mk4/GTI/Jetta product line. This new VR6 improved performance via updated camshafts, variable geometry intake manifold, an increased compression ratio of 10.5:1, and updated emissions equipment. Power increased to 130 kilowatts (177 PS; 174 bhp) at 5,800 rpm, while torque increased to 245 newton metres (181 lbf·ft) at 3,200 rpm. This engine option was available from 1999.5—2002, when it was replaced by the revised 24-valve engine, engine code BDE, at the same time as the European market also introduced this revised engine.

In 2001, the VR6 was enlarged to 3.2 litres, to create a limited-production, high-performance, 168 kilowatts (228 PS; 225 bhp) version of the New Beetle called Beetle RSi. The Beetle RSi was the first production vehicle to use the 3.2 litre24-valve VR6 engine.[citation needed] This engine was later used in the Mk4 Golf R32, and was also introduced in the original Audi TT. According to Volkswagen Group, these variants produced 184 kilowatts (250 PS; 247 bhp) in TT trim (engine ID code: BHE), and 177 kilowatts (241 PS; 237 bhp) in R32 trim (engine ID code: BFH/BML).

In 2005, the European market version of Volkswagen's sixth generation Passat, now with a transverse engine layout, went on sale with a revised version of the 3.2-litre VR6 as its top-spec engine. For North America, the Passat received a new 3.6-litre VR6 with a narrower 10.6 degree cylinder angle, producing 206 kilowatts (280 PS; 276 bhp). These revised 3.2 and 3.6 feature Fuel Stratified Injection (FSI). This new 3.2 FSI VR6 develops 184 kilowatts (250 PS; 247 bhp) at 6,250 rpm, and 330 newton metres (243 lbf·ft)at 3,000 rpm.[8] The introduction of the Passat VR6 also marked the first time a VR6 powered vehicle was made available in North America before Europe.

The first generation Porsche Cayenne base model is powered by a 3.2-liter VR6 engine producing 250 hp (190 kW); modifications in the exhaust manifold allow power to peak at 6700 rpm. This is the same 3.2-liter motor found on a Volkswagen Touareg and Volkswagen R32.

Volkswagen Group has also developed a series of engines which combine two narrow angle "V" cylinder blocks mated together at 72 degrees. These compound VR engines are referred to as "W engines" by VW Group. For example, two VR6 blocks mated together at 72 degrees result in a W12 engine configuration, which is significantly shorter than a 90 degrees V12 engine, but only marginally wider. W8 engine and W16 engine designs were developed in a similar fashion. The W8 uses two four-cylinder "VR4" blocks mated together, and the W16 combines two "VR8" blocks.